Improve emscripten support

[hallucino]

We need to be able to generate a generic emscripten version of PX8 to be able to load cartridges with python + lua support.

[hallucino]

Here an list of items:

• [x] native support with emscripten for the Rust
• [x] include rust cartridge
• [x] include lua cartridge
• [ ] include python cartridge

[hallucino]

All supports works correctly, I need to find a way to add the python cartridge support in emscripten.